The starting battery is primarily charged while driving; if it is full then the second battery charger automatically switches to the second battery. Both the batteries are now charged through the alternator. Up to a total voltage of 12.8 V both the batteries remain connected in parallel. If the voltage falls down below 12.8 V, the two-battery charger automatically switches off the additional battery.Additional consumers should be connected only to the second battery. A safe starting, even after longer shelf life (without charging), remains ensured. Ideal in conjunction with solar systems. The solar modules and the solar charge controllers are simply connected in parallel to the second battery.The electronics is suitable for all 12 V lead-acid batteries. The charging current of an alternator is around 25% of the battery power. For instance, in case of a 100 Ah battery it is 25 A. When the two battery charger is used, this current then distributes itself over the two batteries. The switching capacity of the electronics suffices only for batteries till 500 Ah.